Grinding machine

ABSTRACT

A grinding machine with a stepping motor for feed movements, with a slow pulse generator and a fast pulse generator, and with a control means for introducing pulse from the fast generator during one part of the grinding cycle and from the slow generator during another portion of the grinding cycle.

l l June 17, 1975 3 69l 357 9/l972 McIntosh....l... ,..,......,.....5l/l65.7l

I l GRINDING MACHINE 3.797.l76 Wespi Sl/lUl R Inventor:

Edward G. Robillard, Cherry Valley. Mass,

[73] ASS-Xgme: Cincinnati Milacmmfleald Primary ExuminerHarold D. Whitehead Corporation, Worcester, Mass.

Alromey, Agent, or Firm-Norman S. Blodgett; Gerry A. Blodgett 22 Filed: Dec. 3, 1973 Appl. No.1 421,028

ABSTRACT rinding machine with a stepping motor for feed movements, with a slow pulse generator and a fast pulse generator, and with a control means for intro- 5H165'71 x6577 ducing pulse from the fast generator during one part of the grinding cycle and from the slow generator dur- [56] References and ing another portion of the grinding cycle.

UNITED STATES PATENTS 3,618,269 ll/l97l Robillard...,......vl........u.,... 5l/l65.9 11 Claims, 20 Drawing Figures SHEET PATENTEUJUN 7 I975 FIG. 2

PATENTEDJUH 17 ms FIG. 5 FIG. 9 FIG. [3

FIG. I7

FIG. 6 FIG. IO FIG. I4

FIG. [8

FIG. 7 FIG. II FIG. I5

FIG. I9

FIG. 8 FIG. I2 FIG. I6

GRINDING MACHINE BACKGROUND OF THE INVENTION It has become common practice to use a stepping motor for regulating the transverse movements in a grinding machine. A typical grinding machine of this type is shown in the patent of Robillard US. Pat. No. 3.634.979 which issued on Jan. 18. I972. The stepping rates on feed systems used on such grinders are around 350 steps per second. This rate. when used on a 3-digit feed system at 000050 inch of diameter per step. can be used during the grinding portion of the cycle adequately. However. when the full three digits are used as (during a retraction, dressing. and return cycle portion of the cycle it may take 5.7 seconds to complete the resetting of the wheel. This amount of time. although undesirable. has been accepted in the past on machines in which the workpieces are loaded by hand. When such systems are used on high production machines where the workpieces are automatically loaded and unloaded from the machine. this reset time becomes completely unacceptable. This is even more so when the machine is of the controlled forcetype in which the grinding cycle time has been reduced to a very small amount. In other words, in such machines the amount of the cycle from the time of loading the workpiece to the time of unloading it, is occupied for a very little portion of the cycle time in the actual grinding. The rest of the cycle is devoted to moving the wheel out for a dress and then returning it to finish the grinding portion ofthe cycle. Attempts in the past to overcome this difficulty have been less than successful. because of the inertial loads involved in starting and stopping a wheel head moving at high speed and also because of the difficulty in keeping the stepping motor in step with the train of pulses. These and other difficulties experienced with the prior art devices have been obviated in a novel manner by the present invention.

It is, therefore. an outstanding object of the invention to provide a grinding machine using a stepping motor feed in which relatively long distance travel portions of the grinding cycle are traversed at a high rate of speed.

Another object of this invention is the provision of a stepping motor feed grinding machine in which a low and a high speed pulsing rate is used without difficulties experienced due to shock in changing from one to another.

A further object of the present invention is the provision of a grinding machine having a stepping motor for feed in which changes from low-speed pulsing to highspeed pulsing take place without the stepping motor getting out of step.

It is another object of the instant invention to provide a grinding machine having an interrupt-to-dress cycle in which the portion of the cycle devoted to retraction for dress and to return. is reduced to an acceptable value.

A further object of the invention is the provision of a grinding machine using a pulsing motor feed. in which any interruption of the grinding cycle does not result in loss of synchronization.

With these and other objects in view. as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.

SUMMARY OF THE INVENTION In general. the invention consists of a grinding ma chine having a base. having a workhead slide mounted on the base. having a wheelhead slide mounted on the base. and having a feed mechanism including a step ping motor for producing transverse relative movement between the slides to bring about a grinding cycle. A low-speed pulse generator is provided for producing pulses at a first rate and a high-speed generator is provided for producing pulses at a second rate which is substantially greater than the first rate. A control means is provided for introducing pulses from the lowspeed generator to the stepping motor during a portion of the grinding cycle and for introducing pulses from the high-speed generator to the stepping motor during another portion of the grinding cycle.

More specifically, means is provided for smoothly shifting from one pulse rate to the other without loss of stepping motor synchronization. This means for shifting provides for changing the rate along a selected acceleration curve from the smaller to the larger of the two pulse rates and along a selected deceleration curve from the larger to the smaller.

The control means connects the first pulse generator to the stepping motor to retract the wheel from the workpiece to a base line for treatment by the dressing apparatus and returns it to the workpiece for further grinding. A buffer counter is loaded with a predetermined pulse count to determine the point at which deceleration begins during retraction and again during return. The control means acts to feed the second pulse rate to a down-counter and to the deceleration counter before feeding the second pulse rate to the stepping motor for the retraction movement.

BRIEF DESCRIPTION OF THE DRAWINGS The character of the invention. however. may be best understood by reference to one of its structural forms. as illustrated by the accompanying drawings, in which:

FIG. 1 is a perspective view of a grinding machine embodying the principles of the present invention,

FIG. 2 is an enlarged perspective view of the grinding machine with the covers removed,

FIG. 3 is a sectional view of a portion of the grinding machine taken on the line IllIII of FIG. 4,

FIG. 4 is a plan view of a portion of the grinding machine with parts broken away.

FIGS. 5-19 are electrical schematic diagrams of a control means forming part of the grinding machine, and

FIG. 20 is a diagram showing the manner in which the electrical diagrams of FIGS. 5-19 fit together to make up a complete circuit.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to FIG. 1, wherein are best shown the general features ofthe invention, the grinding machine, indicated generally by the reference numeral 10, is shown as having a base 11 at the upper portion of which is provided with an apron 12. A cover I3 is mounted on the top of the apron and is provided with a window 14 through which the operator can observe the grinding operation. A wheelhead motor 15 is exposed on the top of the base and a control cabinet 16 extends upwardly from the rear of the base. This grind- 

1. A grinding machine, comprising a. a base, b. a workhead slide mounted on the base, c. a wheelhead slide mounted on the base, d. a feed mechanism, including a stepping motor, for producing transverse relative movement between the slides to produce a grinding cycle, e. a first pulse generator having a first section for producing pulses at a first rate and a second section for producing pulses at a second rate which is substantially greater than the first rate, and f. a control means for introducing pulses from the first section to the stepping motor during a portion of the grinding cycle and for introducing pulses from the second section to the stepping motor during another portion of the grinding cycle, the control means including a shifter means operative during an interval when the rate of pulses introduced to the stepping motor is changed between a first value and a second value, to introduce to the stepping motor pulses at rates of smoothly changing value thereby avoiding loss of synchronization between the stepping motor and pulses during the change.
 2. A grinding machine as recited in claim 1, wherein the shifter provides for changing the rate along an acceleration curve from the smaller to the larger of the two pulse rates and along a deceleration curve from the larger to the smaller.
 3. A grinding machine as recited in claim 2, wherein the workhead slide carries a workhead in which a workpiece is mounted for roTation about the axis of an internal surface of revolution that is to be formed on the workpiece, wherein the wheelhead slide carries a wheelhead in which is rotatably mounted a spindle having an abrasive wheel at one end, and wherein a dressing apparatus is mounted for engagement on occasion by the wheel.
 4. A grinding machine as recited in claim 3, wherein the control means connects the pulse generator to the stepping motor to retract the wheel from the workpiece to a base line for treatment by the dressing apparatus and returns it to the workpiece for further grinding.
 5. A grinding machine as recited in claim 4, wherein the retraction movement is started using the first pulse rate, rapidly and smoothly accelerating to the second pulse rate, remaining at the second pulse rate during most of the retraction, and rapidly and smoothly decelerating to the first pulse rate again at the end of the retraction, and wherein the procedure is reversed during the return movement.
 6. A grinding machine as recited in claim 5, wherein a counter is provided for up counting the pulses required to move the wheel from the workpiece to the dressing apparatus and for down counting the pulses to return.
 7. A grinding machine as recited in claim 5, wherein a buffer counter is loaded with a predetermined pulse count to determine the point at which deceleration begins during retraction and again during return.
 8. A grinding machine as recited in claim 7, wherein the control means acts to switch instantaneously from the first pulse rate to the second pulse rate to feed pulses to the deceleration buffer counter.
 9. A grinding machine as recited in claim 7, wherein the control means acts to feed the second pulse rate to a down counter and to the deceleration buffer counter before feeding the second pulse rate to the stepping motor for the retraction movement.
 10. A grinding machine as recited in claim 9, wherein the control means acts after the dressing operation to feed second rate pulses to again load the deceleration buffer counter before feeding second rate pulses to the stepping motor for the return movement.
 11. A grinding machine as recited in claim 1, wherein a feed counter and buffer are provided, the feed counter normally counting the pulses that are introduced to the stepping motor, and the control means being adapted to cause at least one pulse to be counted by the feed counter but stored in the buffer and to be fed to the stepping motor only after the occurrence of a latter event. 